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Bayou orthohantavirus (BAYV) is one of several hantaviruses in the United States that cause hantavirus pulmonary syndrome in humans. Its host reservoir, the marsh rice rat (Oryzomys palustris), inhabits coastal saltmarshes of Louisiana, a region extensively impacted by anthropogenic disturbances, such as the 2010 Deepwater Horizon (DWH) oil spill. The oil spill presents an opportunity to investigate how a large‐scale ecological disturbance can influence the hantavirus host–pathogen dynamic by examining BAYV presence in its reservoir host species in areas with different oiling histories. Here, we: (1) quantify BAYV prevalence in the rice rat in coastal saltmarshes of Louisiana; (2) assess whether prevalence is driven by rice rat demographics, seasonality, or association with habitat characteristics; and (3) determine whether these factors differ by marsh oiling history. We collected mark–recapture data and blood and tissue samples over 5 years (2013–2017) at oiled, unoiled, and reference sites. Testing of the samples for BAYV revealed an antibody and RNA prevalence of 13.7%. Logistic regression analysis found that prevalence varied seasonally and inter‐annually, and in July of 2016 reached 30.8%. Sex (male) and increasing cover of Sporobolus alterniflorus and open water compared to Juncus roemerianus and bare ground were the strongest predictors of hantavirus prevalence. Abundance estimates derived from Huggins closed‐capture models were greatest at oiled sites, but oiling treatment had no residual influence on BAYV prevalence, and abundance and prevalence were not correlated. This study supports the hypothesis that habitat is a main driver of hantavirus prevalence in the host and implies that continued and future disturbances in the region will likely impact the rice rat–BAYV dynamic by altering plant communities and landscape structure. [ABSTRACT FROM AUTHOR]

In 2010, the Deepwater Horizon oil spill released an estimated 4.9 million barrels of oil into the Gulf of Mexico, damaging coastal ecosystems. Seaside Sparrows (Ammospiza maritima)—a year-round resident of Gulf Coast salt marshes—were exposed to oil, as shown by published isotopic and molecular analyses, but fitness consequences have not been clarified. We monitored nests around two bays in Plaquemines Parish, Louisiana, USA from 2012–2017 to assess possible impacts on the nesting biology of Seaside Sparrows. A majority of nests failed (76% of known-fate nests, N = 252 nests, 3521 exposure-days) during our study, and predation was the main cause of nest failure (~91% of failed nests). Logistic exposure analysis revealed that daily nest survival rate: (1) was greater at nests with denser vegetation at nest height, (2) was higher in the more sheltered bay we studied, (3) decreased over the course of the breeding season in each year, and (4) was not correlated with either sediment polycyclic aromatic hydrocarbon concentrations or estimated predator abundance during the years for which we had those data. Although the Deepwater Horizon spill impacted other aspects of Seaside Sparrow ecology, we found no definitive effect of initial oiling or oiled sediment on nest survival during 2012–2017. Because predation was the overwhelming cause of nest failure in our study, additional work on these communities is needed to fully understand demographic and ecological impacts of storms, oil spills, other pollutants, and sea-level rise on Seaside Sparrows and their predators. [ABSTRACT FROM AUTHOR]

Bioindicator species are commonly used as proxies to help identify the ecological effects of oil spills and other stressors. However, the utility of taxa as bioindicators is dependent on understanding their trophic niche and life history characteristics, as these factors mediate their ecological responses. Seaside sparrows (Ammospiza maritima) and marsh rice rats (Oryzomys palustris) are two ubiquitous terrestrial vertebrates that are thought to be bioindicators of oil spills in saltmarsh ecosystems. To improve the utility of these omnivorous taxa as bioindicators, we used carbon and nitrogen stable isotope analysis to quantify their trophic niches at saltmarshes in coastal Louisiana with differing oiling histories. We found that rats generally had lower trophic positions and incorporated more aquatic prey relative to seaside sparrows. The range of resources used (i.e.,trophic niche width) varied based on oiling history. Seaside sparrows had wider trophic niches than marsh rice rats at unoiled sites, but not at oiled sites. Trophic niche widths of conspecifics were less consistent at oiled sites, although marsh rice rats at oiled sites had wider trophic niches than rats at unoiled sites. These results suggest that past oiling histories may have imparted subtle, yet differing effects on the foraging ecology of these two co-occurring species. However, the temporal lag between initial oiling and our study makes identifying the ultimate drivers of differences between oiled and unoiled sites challenging. Even so, our findings provide a baseline quantification of the trophic niches of sympatric seaside sparrows and marsh rice rats that will aid in the use of these species as indicators of oiling and other environmental stressors in saltmarsh ecosystems. [ABSTRACT FROM AUTHOR]

Many bird species exhibit both social monogamy and genetic polygamy. Rates of genetic polygamy (often reported as the proportion of nests containing extra-pair young) in socially monogamous species vary widely, stimulating much research into the potentially adaptive value of these behaviors. Similarly, adult and nestling sex ratios of bird populations are not infrequently male-biased, leading to questions of the adaptive value of a female's ability to influence sex ratios within her nest. Empirical data on both aspects of reproductive behavior, however, are still scarce for a majority of species even within relatively well-studied bird communities. We sampled DNA from nestling (n = 153) and adult (n = 121) Seaside Sparrows (Ammospiza maritima) at 58 nests in southeastern Louisiana from 2012 to 2017. We used microsatellite genotype analyses to discover that (1) ∼32% of nests contained broods with mixed paternity, and (2) ∼4% of broods contained evidence of mixed maternity. We sexed all birds via PCR and found a significant male bias among nestlings (62% of all nestlings were males). Prevalence of mixed paternity and male bias among nestlings did not appear to be related to site oiling status following the Deepwater Horizon oil spill, site context, timing within breeding season, or density of adult Seaside Sparrows or nests. Nonetheless, these results indicate a need for further work to understand the breeding biology of Seaside Sparrows. Muchas especies de aves muestran tanto monogamia social como poligamia genética. Las tasas de poligamia genética (muchas veces reportadas como la proporción de nidos que contienen un polluelo fuera de la pareja) en especies monógamas sociales es muy variable, lo que favorece la investigación en el potencial valor adaptativo de estos comportamientos. De la misma manera, las proporciones de sexo de adultos y de polluelos de las poblaciones de aves no son infrecuentemente sesgadas hacia los machos, lo que lleva a preguntarse sobre el valor adaptativo de la habilidad de la hembra en influir en las proporciones sexuales dentro de su nido. Datos empíricos en ambos aspectos de comportamiento reproductivo, sin embargo, son todavía escasos en la mayoría de especies aún dentro de comunidades de aves relativamente bien estudiadas. Muestreamos ADN de nidadas (n = 153) y adultos (n = 121) de chingolos Ammospiza maritima de 58 nidos del sudeste de Louisiana de 2021 al 2017. Utilizamos análisis genotípicos satelitales para descubrir que (1) ∼32% de los nidos contenían nidadas con paternidad mixta, y alrededor de (2) ∼4% de las nidadas contenían evidencia de maternidad mixta. Determinamos el sexo de todas las aves por medio de PCR y encontramos un sesgo masculino significativo en todas las nidadas (62% de todas las nidadas eran machos). La prevalencia de la paternidad mixta y el sesgo masculino entre las nidadas no parece estar relacionado con el estatus de contaminación del sitio después del derrame de petróleo del Deepwater Horizon, contexto del sitio, temporalidad al interior de la temporada reproductiva o densidad del adulto de chingolos Ammospiza maritima o de nidos. Sin embargo, estos resultados indican una necesidad de estudios posteriores para entender la biología reproductiva de los chingolos Ammospiza marítima. Palabras clave: pantano, Passerellidae, producción fuera de la pareja, reproducción fuera de la pareja, sesgo reproductivo, sistema reproductivo. [ABSTRACT FROM AUTHOR]